It is known in the art to heat the abutting faces of metal parts to forge welding temperature along a line by means of high frequency electrical current supplied to a first contact engaging one part, or the parts, at one end of the line and through a proximity conductor overlying the line, to a second contact engaging the one part, or the parts, at the other end of the line, and then, to force the parts together along the line to form a forge weld between the parts. See, for example, U.S. Pat. No. 3,591,757. In general, the frequency of the current is selected so that when the parts are overlapping, the reference depth of the current in the part nearer the proximity conductor is greater than the thickness of such part. When the parts are in end abutting relation, the reference depth is at least equal the thickness of the abutting ends. The meaning of "reference depth", or "depth of penetration" is set forth in said patent, and reference depths for several metals at current frequencies of 10 KHz and 450 KHz are also set forth in said patent.
The object of the methods set forth in said U.S. Pat. No. 3,591,757 is to weld two metal parts together. There is also a need in the industry to cut larger pieces of metal into smaller pieces, and the edge faces of the smaller pieces need not, in many cases, particularly if the edge faces are to be subsequently welded to another part or parts, be relatively smooth or precisely perpendicular to the major faces of the pieces. In the prior art, the larger piece has been cut or severed by mechanical means, such as by saws or shears, or by gas torches. These processes are relatively slow and use equipment subject to relatively rapid wear or result in undesirable environmental conditions.